Function
Part
Beam splitter
6
Reference
7
Detectors and electronics
8
Signal
9
Flow cell
10
Optical fibers
11
Light source and
monochromator
A Xenon flash lamp gives a high intensity, continuous spectrum throughout the range
160–2000 nm. The light enters a monochromator which includes a condensor, blocking
filter, entrance slit and a concave aberration corrected holographic grating. Monochro-
matic light from the grating is directed to an optical fiber. The grating is turned by a
stepping motor for wavelength selection between 190–700 nm, in steps of 1 nm. Up to
3 wavelengths can be monitored simultaneously.
Blocking filter
For wavelengths between 360–700 nm, a blocking filter is moved into the light path to
filter out unwanted light, half a wavelength from the second order spectrum, before
entering the monochromator.
Beam splitter
The light from the monochromator to the flow cell and from the cell to the detector
electronics is guided by optical fibers. The full intensity of the light is focused on the liquid
flow path, maximizing the sensitivity of the monitor. Before entering the flow cell, the
monochromatic light is split in a beam splitter, with 50% of the light passing through the
sample fiber (S) and the flow cell, and 50% being directed through the reference fiber
(R). Two photodiodes with identical characteristics monitor the intensities of the sample
and reference beams.
28
Monitor UV-900 Operating Instructions 28962214 AD
3 System description
3.3 Monitor principle
